1. Field of the Invention
This invention relates to the manufacture of printing ribbons. More specifically, this invention relates to the manufacture of multi-colored printing ribbons used in wire matrix printers and having portions containing variously colored dye-based inks. The colored portions are separated by a barrier composition which prevents interfusion of the colors.
2. Prior Art
There are two major types of colored inks used in manufacturing colored printing ribbons. One type involves an ink composition containing small particles of insoluble organic or inorganic pigments as the coloring source disbursed in a non-drying oil. Although these pigment-based inks can be utilized to produce multi-colored printing ribbons, the use of pigment-based inks has several disadvantages associated with the pigments. For example, due to the multi-step process required to grind the pigments into the appropriate particle size, pigment-based inks are fairly expensive and difficult to manufacture. Further, the addition of the pigment particles to the vehicle results in a viscous paste-like ink. Thus, pigment-based colored printing ribbons do not readily recover or flow back into those areas of the ribbon previously printed upon. The dispersed pigment particles also cause the print wires in wire matrix printers to abrade and wear quickly. As a result, the printers are subject to increased maintainance.
The other type of colored ink used in manufacturing colored printing ribbons contains, rather than pigments, soluble dyes as the coloring source. Printing inks containing dyes as the coloring source are referred to herein as dye-based inks. These dye-based inks include, by way of example, dyes from the anthaquinone family with one such dye marketed under the trade name "Oil Soluble Blue II" and manufactured by BASF Wyandotte Corporation, and dyes from the nonionic azo family, with three such dyes marketed under the trade names "Sudan Red 7B", "Sudan Deep Black BB" and "Fluoral 5G" and also manufactured by BASF Wyandotte Corporation.
Dye-based inks have several advantages over pigment-based inks when used to produce colored printing ribbons. Such advantages include ready recovery due to their low viscosity and low abrasion and wear rates on the print wires in wire matrix printers due to the absence of particulate matter in the ink. However, the application of dye-based inks to the manufacture of multi-colored printing ribbons has been far from successful. Generally, dye-based inks cannot be used for multi-colored printing ribbons because the different colors on the ribbon quickly interfuse.
While the prior art does recognize the use of barriers in multi-colored printing ribbons, such barriers cause the ribbon to lose its flexibility. This is a significant disadvantage as the printing ribbons used in wire matrix printers flow through a torqued and rough flow path, at times, at very high speed.
One prior art reference, U.S. Pat. No. 2,759,586, does propose several different barriers for preventing interfusion of the colors on multi-colored printing ribbons having dye-based inks; however, those barriers have several disadvantages. For example, those barriers are prepared using solvents, thus necessitating a drying step in their manufacturing process. Several of those barriers specifically use toluene as the solvent; a solvent which cannot be used in many states of the United States as it is an air pollution hazard. Further, several of the barriers contain tricresyl phosphate and a glycerol ester of hydrogenated rosin; ingredients which cause the final product ribbon to be tacky. Tricresyl phosphate also would tend to dissolve some of the plastic components of wire matrix printers which contact the printing ribbon. Further still, the claimed barriers containing nitro cellulose and cellulose acetate have little, if any, adhesive properties and, as a result, those barriers cannot be sealed onto the ribbon's base material under flexing conditions.
Thus, there is a great need for flexible multi-colored printing ribbons which use dye-based inks, but where interfusion of the different colors is satisfactorily prevented. There is a further need for such a ribbon which retains the flexibility required in wire matrix printers.
Accordingly, the main object of the present invention is to provide a multi-colored printing ribbon in which the dye-based colors are satisfactorily prevented from interfusing without causing an adverse effect on the flexibility of the ribbon and which minimizes the abrasion and wear rate of the print wires in wire matrix printers.
The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation, together with further objectives and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as definition of the limits of the invention.